Modern military engines operate with turbine outlet temperatures that are ever higher, thereby leading to temperatures at the nozzle flaps that are ever higher when operating in post-combustion modes. The maximum temperature limit of conventional materials has already been reached. In order to give flaps a suitable lifetime, it is therefore necessary to keep them at a temperature below such limits.
The increase in flap temperature also has the effect of increasing the infrared signature of the solid portions of the engine. To ensure that the airplane remains suitably discreet, or to make it more discreet, it is also necessary to reduce this temperature.
The use of the flow of secondary air downstream from the thermal protection lining is the means that avoids losing energy in order to cool the nozzle flaps by convection.
However, the transmission of this flow between the stationary portions of the post-combustion chamber and the moving portions of the nozzle must be performed in a manner that is as leak tight as possible.
U.S. Pat. No. 4,645,217 discloses a flexible sealing gasket disposed between the casing of the post-combustion chamber and an axially movable cylindrical sleeve supporting the flaps. This gasket sliding on the sleeve and fixed to the casing is constituted by two superposed plates having axial slots in alternation, and by a fabric that withstands high temperatures, interposed between the two plates. The ends of portions of one plate disposed between two consecutive slots are curved onto the edge of the other plate in order to enclose the fabric. That document does not teach that that type of gasket is capable of providing satisfactory sealing between a stationary annular part and a set of flaps hinged on said part.